The involvement of cysteine proteases and protease inhibitor genes in the regulation of programmed cell death in plants

A Bowman-Birk type protease inhibitor is involved in the tolerance to salt stress in wheat

A salt-responsive gene WRSI5 was characterized from salt-tolerant cultivar Shanrong No. 3 (SR3), an introgression line via asymmetric somatic hybrid between Triticum aestivum L. cv. Jinan177 (JN177) and Thinopyrum ponticum Podp. The peptide encoded by WRSI5 contains a Bowman-Birk domain sharing a high level of sequence identity to monocotyledonous protease inhibitors. When expressed in vitro, the WRSI5 gene product exhibited trypsin, but not chymotrypsin inhibition. The expression level of WRSI5 was increased in SR3 roots exposed to salt, drought or oxidative stress. In situ hybridization showed that it is induced in the endodermal cells of the mature region of the SR3 root tip, with no signal detectable in the corresponding region of the salt-susceptible cultivar JN177. SR3 has a higher selectivity for K(+) over Na(+), and therefore limits the transport of Na(+) from the root to the shoot. When overexpressed in Arabidopsis thaliana, WRSI5 improves the ability of seedlings to grow on a medium containing 150 mM NaCl. We suggest that WRSI5 plays an important role in regulating the plant growth rate or long-distance Na(+) transport in SR3 plants exposed to salt stress.

Arabidopsis protein disulfide isomerase-5 inhibits cysteine proteases during trafficking to vacuoles before programmed cell death of the endothelium in developing seeds

Protein disulfide isomerase (PDI) oxidizes, reduces, and isomerizes disulfide bonds, modulates redox responses, and chaperones proteins. The Arabidopsis thaliana genome contains 12 PDI genes, but little is known about their subcellular locations and functions. We demonstrate that PDI5 is expressed in endothelial cells about to undergo programmed cell death (PCD) in developing seeds. PDI5 interacts with three different Cys proteases in yeast two-hybrid screens. One of these traffics together with PDI5 from the endoplasmic reticulum through the Golgi to vacuoles, and its recombinant form is functionally inhibited by recombinant PDI5 in vitro. Peak PDI5 expression in endothelial cells precedes PCD, whereas decreasing PDI5 levels coincide with the onset of PCD-related cellular changes, such as enlargement and subsequent collapse of protein storage vacuoles, lytic vacuole shrinkage and degradation, and nuclear condensation and fragmentation. Loss of PDI5 function leads to premature initiation of PCD during embryogenesis and to fewer, often nonviable, seeds. We propose that PDI5 is required for proper seed development and regulates the timing of PCD by chaperoning and inhibiting Cys proteases during their trafficking to vacuoles before PCD of the endothelial cells. During this transitional phase of endothelial cell development, the protein storage vacuoles become the de facto lytic vacuoles that mediate PCD.

RD19, an Arabidopsis cysteine protease required for RRS1-R-mediated resistance, is relocalized to the nucleus by the Ralstonia solanacearum PopP2 effector

Bacterial wilt, a disease impacting cultivated crops worldwide, is caused by the pathogenic bacterium Ralstonia solanacearum. PopP2 (for Pseudomonas outer protein P2) is an R. solanacearum type III effector that belongs to the YopJ/AvrRxv protein family and interacts with the Arabidopsis thaliana RESISTANT TO RALSTONIA SOLANACEARUM 1-R (RRS1-R) resistance protein. RRS1-R contains the Toll/Interleukin1 receptor-nucleotide binding site-Leu-rich repeat domains found in several cytoplasmic R proteins and a C-terminal WRKY DNA binding domain. In this study, we identified the Arabidopsis Cys protease RESPONSIVE TO DEHYDRATION19 (RD19) as being a PopP2-interacting protein whose expression is induced during infection by R. solanacearum. An Arabidopsis rd19 mutant in an RRS1-R genetic background is compromised in resistance to the bacterium, indicating that RD19 is required for RRS1-R-mediated resistance. RD19 normally localizes in mobile vacuole-associated compartments and, upon coexpression with PopP2, is specifically relocalized to the plant nucleus, where the two proteins physically interact. No direct physical interaction between RRS1-R and RD19 in the presence of PopP2 was detected in the nucleus as determined by Förster resonance energy transfer. We propose that RD19 associates with PopP2 to form a nuclear complex that is required for activation of the RRS1-R-mediated resistance response.

The origin and evolution of plant cystatins and their target cysteine proteinases indicate a complex functional relationship

BACKGROUND

Cystatins and their putative targets, the families of cysteine proteinases C1A and C13 play key roles in plants. Comparative genomic analyses are powerful tools to obtain valuable insights into the conservation and evolution of the proteinases and their proteinaceous inhibitors, and could aid to elucidate issues concerning the function of these proteins.

RESULTS

We have performed an evolutionary comparative analysis of cysteine proteinases C1A and C13 and their putative inhibitors in representative species of different taxonomic groups that appeared during the evolution of the Viridiplantae. The results indicate that whereas C1A cysteine proteinases are present in all taxonomic groups, cystatins and C13 cysteine proteinases are absent in some basal groups. Moreover, gene duplication events have been associated to the increasing structural and functional complexities acquired in land plants.

CONCLUSION

Comparative genomic analyses have provided us valuable insights into the conservation and evolution of the cystatin inhibitory family and their putative targets, the cysteine proteinases from families C1A and C13. Functionality of both families of proteins in plants must be the result of a coevolutionary process that might have occurred during the evolution of basal and land plants leading to a complex functional relationship among them.

The Cladosporium fulvum virulence protein Avr2 inhibits host proteases required for basal defense

Cladosporium fulvum (syn. Passalora fulva) is a biotrophic fungal pathogen that causes leaf mold of tomato (Solanum lycopersicum). During growth in the apoplast, the fungus establishes disease by secreting effector proteins, 10 of which have been characterized. We have previously shown that the Avr2 effector interacts with the apoplastic tomato Cys protease Rcr3, which is required for Cf-2-mediated immunity. We now show that Avr2 is a genuine virulence factor of C. fulvum. Heterologous expression of Avr2 in Arabidopsis thaliana causes enhanced susceptibility toward extracellular fungal pathogens, including Botrytis cinerea and Verticillium dahliae, and microarray analysis showed that Avr2 expression triggers a global transcriptome reflecting pathogen challenge. Cys protease activity profiling showed that Avr2 inhibits multiple extracellular Arabidopsis Cys proteases. In tomato, Avr2 expression caused enhanced susceptibility toward Avr2-defective C. fulvum strains and also toward B. cinerea and V. dahliae. Cys protease activity profiling in tomato revealed that, in this plant also, Avr2 inhibits multiple extracellular Cys proteases, including Rcr3 and its close relative Pip1. Finally, silencing of Avr2 significantly compromised C. fulvum virulence on tomato. We conclude that Avr2 is a genuine virulence factor of C. fulvum that inhibits several Cys proteases required for plant basal defense.

Isolation and characterization of a cDNA encoding a papain-like cysteine protease from alfalfa

Protein hydrolyzation is activated and involved in response to various stress signals. In the present study, a full-length cDNA, named MsCP1, encoding a papain-like cysteine protease was obtained by degenerated primers and 3'- and 5'-RACE from salt-tolerant alfalfa. The cDNA contained an open reading frame encoding a deduced protein of 350 amino acids with a putative N-terminal signal peptide, NPIR vacuole-sorting signal sequence and potential N-linked glycosylation sites. The deduced sequence showed a high similarity to deduced proteins from pea, tobacco, tomato and ryegrass. Fusion expression analysis in Escherichia coli showed that the putative eukaryotic signal peptide prevented its expression in prokaryotic system. The integration and transcript of the expression elements in transgenic tobacco plants were detected with Southern blot and RT-PCR analysis.

Transcriptome profiling identified novel genes associated with aluminum toxicity, resistance and tolerance in Medicago truncatula

Oligonucleotide microarrays corresponding to over 16,000 genes were used to analyze changes in transcript accumulation in root tips of the Al-sensitive Medicago truncatula cultivar Jemalong genotype A17 in response to Al treatment. Out of 2,782 genes with significant changes in transcript accumulation, 324 genes were up-regulated and 267 genes were down-regulated at least twofold by Al. Up-regulated genes were enriched in transcripts involved in cell-wall modification and abiotic and biotic stress responses while down-regulated genes were enriched in transcripts involved in primary metabolism, secondary metabolism, protein synthesis and processing, and the cell cycle. Known markers of Al-induced gene expression including genes associated with oxidative stress and cell wall stiffening were differentially regulated in this study. Transcript profiling identified novel genes associated with processes involved in Al toxicity including cell wall modification, cell cycle arrest and ethylene production. Novel genes potentially associated with Al resistance and tolerance in M. truncatula including organic acid transporters, cell wall loosening enzymes, Ca(2+) homeostasis maintaining genes, and Al-binding were also identified. In addition, expression analysis of nine genes in the mature regions of the root revealed that Al-induced gene expression in these regions may play a role in Al tolerance. Finally, interfering RNA-induced silencing of two Al-induced genes, pectin acetylesterase and annexin, in A17 hairy roots slightly increased the sensitivity of A17 to Al suggesting that these genes may play a role in Al resistance.

Identification of peptidases in Nicotiana tabacum leaf intercellular fluid

Peptidases in the extracellular space might affect the integrity of recombinant proteins expressed in, and secreted from, plant cells. To identify extracellular peptidases, we recovered the leaf intercellular fluid from Nicotiana tabacum plants by an infiltration-centrifugation method. The activity of various peptidases was detected by an in vitro assay in the presence of specific inhibitors, using BSA and human serum gamma-globulin as substrates. Peptidases were detected by 1- and 2-D zymography in a polyacrylamide gel containing gelatin as substrate. Proteolytic activity was observed over a wide range of molecular masses equal to, or higher than, 45 kDa. To identify the peptidases, the extracellular proteins were digested with trypsin and analyzed by LC and MS. Seventeen peptides showing identity or similarity to predicted plant aspartic, cysteine, and serine peptidases have been identified. The extracellular localization of a cysteine peptidase aleurain homolog was also shown.

Kunitz trypsin inhibitor: an antagonist of cell death triggered by phytopathogens and fumonisin b1 in Arabidopsis

Programmed cell death (PCD) is a central regulatory process in both plant development and in plant responses to pathogens. PCD requires a coordinate activation of pro-apoptotic factors such as proteases and suppressors inhibiting and modulating these processes. In plants, various caspase-like cysteine proteases as well as serine proteases have been implicated in PCD. Here, we show that a serine protease (Kunitz trypsin) inhibitor (KTI1) of Arabidopsis acts as a functional KTI when produced in bacteria and in planta. Expression of AtKTI1 is induced late in response to bacterial and fungal elicitors and to salicylic acid. RNAi silencing of the AtKTI1 gene results in enhanced lesion development after infiltration of leaf tissue with the PCD-eliciting fungal toxin fumonisin B1 (FB1) or the avirulent bacterial pathogen Pseudomonas syringae pv tomato DC3000 carrying avrB (Pst avrB). Overexpression of AtKTI1 results in reduced lesion development after Pst avrB and FB1 infiltration. Interestingly, RNAi silencing of AtKTI1 leads to enhanced resistance to the virulent pathogen Erwinia carotovora subsp. carotovora SCC1, while overexpression of AtKTI1 leads to higher susceptibility towards this pathogen. Together, these data indicate that AtKTI1 is involved in modulating PCD in plant-pathogen interactions.

[Reactive oxygen species, stress and cell death in plants]

Plants are constantly exposed to changes in environmental conditions. During periods of stress, the cellular redox homeostasis is altered as a result of reactive oxygen species accumulation. The change in redox is responsible for the symptoms commonly observed during periods of stress and reflects the phytotoxic nature of oxygen radical accumulation. However, oxygen radicals have recently been identified as key actors in the response to stress and their role as secondary messengers is now clearly established. The identification of their role in gene regulation has allowed one to identify them as key regulators in the induction and execution of programmed cell death typically observed during developmental processes as well as during stress responses. This review presents recent advances in the characterisation of the role of reactive oxygen species in plants.

Dormancy in potato tuber meristems: chemically induced cessation in dormancy matches the natural process based on transcript profiles

Meristem dormancy in perennial plants is a developmental process that results in repression of metabolism and growth. The cessation of dormancy results in rapid growth and should be associated with the production of nascent transcripts that encode for gene products controlling for cell division and growth. Dormancy cessation was allowed to progress normally or was chemically induced using bromoethane (BE), and microarray analysis was used to demonstrate changes in specific transcripts in response to dormancy cessation before a significant increase in cell division. Comparison of normal dormancy cessation to BE-induced dormancy cessation revealed a commonality in both up and downregulated transcripts. Many transcripts that decrease as dormancy terminates are inducible by abscisic acid particularly in the conserved BURP domain proteins, which include the RD22 class of proteins and in the storage protein patatin. Transcripts that are associated with an increase in expression encoded for proteins in the oxoglutarate-dependent oxygenase family. We conclude that BE-induced cessation of dormancy initiates transcript profiles similar to the natural processes that control dormancy.

Substrate Specificity of a Cationic Peptidase from Bromelia Hemisphaerica L

A cationic peptidase, named hemisphaericin-C, has been purified from the juice of Bromelia hemisphaerica fruits by ammonium sulfate precipitation, gel filtration on Sephadex G-75 and cationic exchange chromatography on carboxymethyl cellulose (CMC), to yield a single 24 kDa band on SDS-polyacrylamide gel electrophoresis (SDS-PAGE), which showed esterase and proteolytic activities. The esterase activity was inhibited by E-64, leupeptin, and cystatin, but not by EDTA. Characterization of the primary specificity of hemisphaericin-C showed activity towards substrates specific for chymotrypsin: N-succinyl-L-Phe- p-nitroanilide (PHE pNA) and N-benzoyl-L-Tyr- p-nitroanilide (TYR pNA), and those for trypsin: N-benzoyl-L-arg- p-nitroanilide (BA pNA) to a lower degree. The higher selectivity, assessed by Vmax/Km, was obtained for PHE pNA, the substrate containing the aromatic lateral chain amino acid at the P1 position. The preference of hemisphaericin-C for PHE pNA gives a clue in the search for a chymotrypsin-like peptidase from a vegetal source.

The hypersensitive response; the centenary is upon us but how much do we know?

With the centenary of the first descriptions of 'hypersensitiveness' following pathogenic challenge upon us, it is appropriate to assess our current understanding of the hypersensitive response (HR) form of cell death. In recent decades our understanding of the initiation, associated signalling, and some important proteolytic events linked to the HR has dramatically increased. Genetic approaches are increasingly elucidating the function of the HR initiating resistance genes and there have been extensive analyses of death-associated signals, calcium, reactive oxygen species (ROS), nitric oxide, salicylic acid, and now sphingolipids. At the same time, attempts to draw parallels between mammalian apoptosis and the HR have been largely unsuccessful and it may be better to consider the HR to be a distinctive form of plant cell death. We will consider if the HR form of cell death may occur through metabolic dysfunction in which malfunctioning organelles may play a major role. This review will highlight that although our knowledge of parts of the HR is excellent, a comprehensive molecular model is still to be attained.

Involvement of polyamine oxidase in wound healing

Hydrogen peroxide (H(2)O(2)) is involved in plant defense responses that follow mechanical damage, such as those that occur during herbivore or insect attacks, as well as pathogen attack. H(2)O(2) accumulation is induced during wound healing processes as well as by treatment with the wound signal jasmonic acid. Plant polyamine oxidases (PAOs) are H(2)O(2) producing enzymes supposedly involved in cell wall differentiation processes and defense responses. Maize (Zea mays) PAO (ZmPAO) is a developmentally regulated flavoprotein abundant in primary and secondary cell walls of several tissues. In this study, we investigated the effect of wounding on ZmPAO gene expression in the outer tissues of the maize mesocotyl and provide evidence that ZmPAO enzyme activity, protein, and mRNA levels increased in response to wounding as well as jasmonic acid treatment. Histochemically detected ZmPAO activity especially intensified in the epidermis and in the wound periderm, suggesting a tissue-specific involvement of ZmPAO in wound healing. The role played by ZmPAO-derived H(2)O(2) production in peroxidase-mediated wall stiffening events was further investigated by exploiting the in vivo use of N-prenylagmatine (G3), a selective and powerful ZmPAO inhibitor, representing a reliable diagnostic tool in discriminating ZmPAO-mediated H(2)O(2) production from that generated by peroxidase, oxalate oxidase, or by NADPH oxidase activity. Here, we demonstrate that G3 inhibits wound-induced H(2)O(2) production and strongly reduces lignin and suberin polyphenolic domain deposition along the wound, while it is ineffective in inhibiting the deposition of suberin aliphatic domain. Moreover, ZmPAO ectopic expression in the cell wall of transgenic tobacco (Nicotiana tabacum) plants strongly enhanced lignosuberization along the wound periderm, providing evidence for a causal relationship between PAO and peroxidase-mediated events during wound healing.

Cysteine proteinases regulate chloroplast protein content and composition in tobacco leaves: a model for dynamic interactions with ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) vesicular bodies

The roles of cysteine proteinases (CP) in leaf protein accumulation and composition were investigated in transgenic tobacco (Nicotiana tabacum L.) plants expressing the rice cystatin, OC-1. The OC-1 protein was present in the cytosol, chloroplasts, and vacuole of the leaves of OC-1 expressing (OCE) plants. Changes in leaf protein composition and turnover caused by OC-1-dependent inhibition of CP activity were assessed in 8-week-old plants using proteomic analysis. Seven hundred and sixty-five soluble proteins were detected in the controls compared to 860 proteins in the OCE leaves. A cyclophilin, a histone, a peptidyl-prolyl cis-trans isomerase, and two ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase isoforms were markedly altered in abundance in the OCE leaves. The senescence-related decline in photosynthesis and Rubisco activity was delayed in the OCE leaves. Similarly, OCE leaves maintained higher leaf Rubisco activities and protein than controls following dark chilling. Immunogold labelling studies with specific antibodies showed that Rubisco was present in Rubisco vesicular bodies (RVB) as well as in the chloroplasts of leaves from 8-week-old control and OCE plants. Western blot analysis of plants at 14 weeks after both genotypes had flowered revealed large increases in the amount of Rubisco protein in the OCE leaves compared to controls. These results demonstrate that CPs are involved in Rubisco turnover in leaves under optimal and stress conditions and that extra-plastidic RVB bodies are present even in young source leaves. Furthermore, these data form the basis for a new model of Rubisco protein turnover involving CPs and RVBs.

Phytotoxic Nep1-like proteins from the necrotrophic fungus Botrytis cinerea associate with membranes and the nucleus of plant cells

Nep1-like proteins (NLPs), produced by an array of unrelated microorganisms, are phytotoxic for dicotyledonous plant cells but their mode of action has not yet been established. Two paralogous NLPs from the necrotrophic plant pathogenic fungus Botrytis cinerea were characterized, designated BcNEP1 and BcNEP2. Both proteins were produced in the heterologous host Pichia pastoris and purified to homogeneity. The localization of fluorescently labelled proteins was studied and mechanisms of cell death were investigated in protoplasts and suspension cells. Purified BcNEP1 and BcNEP2 caused necrosis in all dicotyledonous plant species tested, but not in monocotyledons. A synthetic heptapeptide comprising a sequence (GHRHDWE) that is conserved in all NLPs did not cause symptoms and was unable to interfere with necrosis induction by BcNEP1 and BcNEP2 proteins. Fluorescently labelled BcNEP1 and BcNEP2 proteins were associated with plasma membranes and the nuclear envelope, as well as in the nucleolus of responding plant cells. A strong hydrogen peroxide (H(2)O(2)) accumulation was observed in chloroplasts. The death process was characterized by TUNEL assays as apoptosis, necrosis or intermediate forms of both. BcNEP1- and BcNEP2-induced cell death execution could not be abolished by specific inhibitors. These results provide further information on mechanisms of NLP-inflicted cell death.

Apoptotic-like programmed cell death in plants

Programmed cell death (PCD) is now accepted as a fundamental cellular process in plants. It is involved in defence, development and response to stress, and our understanding of these processes would be greatly improved through a greater knowledge of the regulation of plant PCD. However, there may be several types of PCD that operate in plants, and PCD research findings can be confusing if they are not assigned to a specific type of PCD. The various cell-death mechanisms need therefore to be carefully described and defined. This review describes one of these plant cell death processes, namely the apoptotic-like PCD (AL-PCD). We begin by examining the hallmark 'apoptotic-like' features (protoplast condensation, DNA degradation) of the cell's destruction that are characteristic of AL-PCD, and include examples of AL-PCD during the plant life cycle. The review explores the possible cellular 'executioners' (caspase-like molecules; mitochondria; de novo protein synthesis) that are responsible for the hallmark features of the cellular destruction. Finally, senescence is used as a case study to show that a rigorous definition of cell-death processes in plant cells can help to resolve arguments that occur in the scientific literature regarding the timing and control of plant cell death.

Programmed cell death in plants: new insights into redox regulation and the role of hydrogen peroxide

Programmed cell death (PCD), the highly regulated dismantling of cells, is essential for plant growth and survival. PCD plays key roles in embryo development, formation and maturation of many cell types and tissues, and plant reaction/adaptation to environmental conditions. Reactive oxygen species (ROS) are not only toxic by products of aerobic metabolism with strictly controlled cellular levels, but they also function as signaling agents regulating many biological processes and producing pleiotropic effects. Over the last decade, ROS have become recognized as important modulators of plant PCD. Molecular genetic approaches using plant mutants and transcriptome studies related to ROS-mediated PCD have revealed a wide array of plant-specific cell death regulators and have contributed to unraveling the elaborate redox signaling network. This review summarizes the biological processes, in which plant PCD participates and discusses the signaling functions of ROS with emphasis on hydrogen peroxide.

A comparative proteomic analysis of tomato leaves in response to waterlogging stress

A comparative proteomic approach has been adopted in combination with physiological and biochemical analysis of tomato leaves responding to waterlogging stress. Waterlogging resulted in increases of relative ion leakage, lipid peroxidation and in vivo H2O2 content, whereas the chlorophyll content was decreased. Histocytochemical investigations with 3,3'-diaminobenzidine to localize H2O2 and Evans blue to detect dead cells suggested that oxidative stress has a significant role to leaf senescence. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the most abundant leaf protein, was successfully reduced from the samples by a fractionation method based on 15% polyethylene glycol (PEG). Elimination of Rubisco was further confirmed by Western blot analysis. To elucidate the temporal changes of the protein patterns in tomato leaves, the total soluble and the PEG-fractionated proteins were separated by two-dimensional electrophoresis (2-DE) and visualized by Coomassie Brilliant Blue staining. A total of 52 protein spots were differentially expressed, wherein 33 spots were identified by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry or electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis. The identified proteins are involved in several processes, i.e. photosynthesis, disease resistance, stress and defense mechanisms, energy and metabolism and protein biosynthesis. Results from 2-DE analysis, combined with immunoblotting clearly showed that the fragments of Rubisco large subunit were significantly degraded. This could result from a higher production of reactive oxygen species in leaves under waterlogging stress. Furthermore, four differentially accumulated proteins were analyzed at the mRNA level, confirming the differential gene expression levels and revealing that transcription levels are not always concomitant to the translation level. A number of novel proteins were differentially expressed or appeared only in the PEG-fractionated protein samples, indicating that PEG fractionation system can be used as a versatile protein fractionation technique in proteomic analysis to identify novel or low-abundant proteins from all kinds of plant species.

Identification of cysteine proteases and screening of cysteine protease inhibitors in biological samples by a two-dimensional gel system of zymography and reverse zymography

We have developed a two-dimensional (2D-) gel system of zymography and reverse zymography for the detection and characterization of proteases and protease inhibitors. Isoelectric focusing (IEF) agarose gels with pH gradients were employed for separation in the first-dimension and sodium dodecyl sulfate (SDS)-polyacrylamide gel copolymerized with gelatin used for the second dimension. Proteases and protease inhibitors separated by IEF gel were applied on the second gel without trichloroacetic acid (TCA) fixation. Protease activity in the 2D-gel was visualized as transparent spots where gelatin substrate was digested after commassie brilliant blue (CBB) staining. Some of the transparent spots from the skin mucus extract of rainbow trout were determined to be a cysteine protease through use of E-64 or CA-074. In the reverse zymography technique, the gel was incubated with papain solution at 37 degrees C for 18 h. Cysteine protease inhibitors from broad bean seeds were detected as clear blue spots after CBB staining. The amino (N-) terminal sequences of four papain inhibitor spots thus detected were demonstrated to be identical to that of favin beta chain, a broad bean lectin. Taken together, our system can be considered to be an efficient technique for discovering and characterizing new proteases and protease inhibitors in biological samples. This is the first report describing a 2D-gel system of zymography and reverse zymography.

Identification of Cysteine Proteases and Screening of Cysteine Protease Inhibitors in Biological Samples by a Two-Dimensional Gel System of Zymography and Reverse Zymography

We have developed a two-dimensional (2D-) gel system of zymography and reverse zymography for the detection and characterization of proteases and protease inhibitors. Isoelectric focusing (IEF) agarose gels with pH gradients were employed for separation in the first-dimension and sodium dodecyl sulfate (SDS)-polyacrylamide gel copolymerized with gelatin used for the second dimension. Proteases and protease inhibitors separated by IEF gel were applied on the second gel without trichloroacetic acid (TCA) fixation. Protease activity in the 2D-gel was visualized as transparent spots where gelatin substrate was digested after commassie brilliant blue (CBB) staining. Some of the transparent spots from the skin mucus extract of rainbow trout were determined to be a cysteine protease through use of E-64 or CA-074. In the reverse zymography technique, the gel was incubated with papain solution at 37°C for 18 h. Cysteine protease inhibitors from broad bean seeds were detected as clear blue spots after CBB staining. The amino (N-) terminal sequences of four papain inhibitor spots thus detected were demonstrated to be identical to that of favin β chain, a broad bean lectin. Taken together, our system can be considered to be an efficient technique for discovering and characterizing new proteases and protease inhibitors in biological samples. This is the first report describing a 2D-gel system of zymography and reverse zymography.

A proteomic approach in analyzing heat-responsive proteins in rice leaves

The present study investigated rice leaf proteome in response to heat stress. Rice seedlings were subjected to a temperature of 42 degrees C and samples were collected 12 and 24 h after treatment. Increased relative ion leakage and lipid peroxidation suggested that oxidative stress frequently was generated in rice leaves exposed to high temperature. 2-DE, coupled with MS, was used to investigate and identify heat-responsive proteins in rice leaves. In order to identify the low-abundant proteins in leaves, samples were prefractionated by 15% PEG. The PEG supernatant and the pellet fraction samples were separated by 2-DE, and visualized by silver or CBB staining. Approximately 1000 protein spots were reproducibly detected on each gel, wherein 73 protein spots were differentially expressed at least at one time point. Of these differentially expressed proteins, a total of 34 and 39 protein spots were found in the PEG supernatant and pellet fractions, respectively. Using MALDI-TOF MS, a total of 48 proteins were identified. These proteins were categorized into classes related to heat shock proteins, energy and metabolism, redox homeostasis, and regulatory proteins. The results of the present study show that a group of low molecular small heat shock proteins (sHSPs) were newly induced by heat stress. Among these sHSPs, a low molecular weight mitochondrial (Mt) sHSP was validated further by Western blot analysis. Furthermore, four differentially accumulated proteins that correspond to antioxidant enzymes were analyzed at the mRNA level, which confirmed the differential gene expression levels, and revealed that transcription levels were not completely concomitant with translation. The identification of some novel proteins in the heat stress response provides new insights that can lead to a better understanding of the molecular basis of heat-sensitivity in plants.

MALE STERILITY1 is required for tapetal development and pollen wall biosynthesis

The Arabidopsis thaliana MALE STERILITY1 (MS1) gene is critical for viable pollen formation and has homology to the PHD-finger class of transcription factors; however, its role in pollen development has not been fully defined. We show that MS1 transcription appears to be autoregulated by the wild-type MS1 transcript or protein. Using a functional green fluorescent protein (GFP) fusion to analyze the temporal and spatial expression of MS1, we demonstrate that the MS1:GFP protein is nuclear localized within the tapetum and is expressed in a developmentally regulated manner between late tetraspore and microspore release, then rapidly breaks down, probably by ubiquitin-dependent proteolysis. Absence of MS1 expression results in changes in tapetal secretion and exine structure. Microarray analysis has shown that 260 (228 downregulated and 32 upreglated) genes have altered expression in young ms1 buds. These genes are primarily associated with pollen wall and coat formation; however, a number of transcription factors and Cys proteases have also been identified as the putative primary regulatory targets of MS1. Ectopic expression of MS1 alters transcriptional regulation of vegetative gene expression, resulting in stunted plants with increased levels of branching, partially fertile flowers and an apparent increase in wall material on mature pollen. MS1 therefore plays a critical role in the induction of pollen wall and pollen coat materials in the tapetum and, ultimately, the production of viable pollen.

Protein changes in the albedo of citrus fruits on postharvesting storage

In this work, major protein changes in the albedo of the fruit peel of Murcott tangor (tangerine x sweet orange) during postharvest ageing were studied through 2D PAGE. Protein content in matured on-tree fruits and in fruits stored in nonstressing [99% relative humidity (RH) and 25 degrees C], cold (99% RH and 4 degrees C), and drought (60% RH and 25 degrees C) conditions was initially determined. Protein identification through MS/MS determinations revealed in all samples analyzed the occurrence of manganese superoxide dismutase (Mn SOD), actin, ATP synthase beta subunit (ATPase), citrus salt-stress associated protein (CitSap), ascorbate peroxidase (APX), translationally controlled tumor protein (TCTP), and a cysteine proteinase (CP) of the papain family. The latter protein was identified in two different gel spots, with different molecular mass, suggesting the simultaneous presence of the proteinase precursor and its active form. While Mn SOD, actin, ATPase, and CitSap were unchanged in the assayed conditions, TCTP and APX were downregulated during the postharvest ageing process. Ageing-induced APX repression was also reversed by drought. CP contents in albedo, which were similar in on- and off-tree fruits, were strongly dependent upon cold storage. The active/total CP protein ratio significantly increased after cold exposure. This proteomic survey indicates that major changes in protein content in the albedo of the peel of postharvest stored citrus fruits are apparently related to the activation of programmed cell death (PCD).

Transcriptional profiling of indica rice cultivar IET8585 (Ajaya) infected with bacterial leaf blight pathogen Xanthomonas oryzae pv oryzae

An indica rice cultivar IET8585 (Ajaya) resists diverse races of the Xanthomonas oryzae pv oryzae pathogen attack, and is often cultivated as bacterial leaf blight (blb) resistant check in India. Earlier we reported a recessive blb resistance gene mapped to the long arm of chromosome 5 in IET8585. Recessive gene-mediated blb resistance mechanism is not yet clearly understood. Here we analyzed the transcriptional profile of the blb infected resistant cultivar by rice 22K oligo array. Microarray analysis revealed differential expression of numerous genes at both early (6 h) and late (120 h) stages of infection in the resistant IET8585 cultivar over the susceptible IR24. Some of the differential gene expressions were validated by both RT-PCR and Western blot analysis. Higher expression of ethylene response element binding protein (EREBP) transcription factor along with lower expression of alcohol dehydrogenase gene and reactive oxygen species (ROS) scavenging system may be responsible for hypersensitive cell death in the resistant cultivar upon bacterial infection. Induction of glutathione-mediated detoxification and flavonoid biosynthetic pathways along with up-regulation of defense genes during infection may inhibit pathogen spread in the host tissues. In light of this and previous studies a mechanism of recessive gene-mediated bacterial blight resistance in indica rice is discussed.

Purification and characterization of a trypsin-papain inhibitor from Pithecelobium dumosum seeds and its in vitro effects towards digestive enzymes from insect pests

A novel trypsin-papain inhibitor, named PdKI-2, was purified from the seeds of Pithecelobium dumosum seeds by TCA precipitation, Trypsin-Sepharose chromatography and reversed-phase HPLC. PdKI-2 had an M(r) of 18.1 kDa as determined by SDS-PAGE and was composed of a single polypeptide chain. The inhibition on trypsin was stable at pH range 2-10, temperature of 50 degrees C and had a K(i) value of 1.65 x 10(-8)M, with a competitive inhibition mechanism. PdKI-2 was also active to papain, a cysteine proteinase, and showed a noncompetitive inhibition mechanism and K(i) value of 5.1 x 10(-7)M. PdKI-2 was effective against digestive proteinase from bruchids Zabrotes subfasciatus and Callosobruchus maculatus; Dipteran Ceratitis capitata; Lepidopterans Plodia interpunctella and Alabama argillacea, with 74.5%, 70.0%, 70.3%, 48.7%, and 13.6% inhibition, respectively. Results support that PdKI-2 is a member of Kunitz-inhibitor family and its effect on digestive enzyme larvae from diverse orders indicated this protein as a potent insect antifeedant.

Expression of a metacaspase gene of Nicotiana benthamiana after inoculation with Colletotrichum destructivum or Pseudomonas syringae pv. tomato, and the effect of silencing the gene on the host response

Metacaspases are cysteine proteinases that have homology to caspases, which play a central role in signaling and executing programmed cell death in animals. A type II metacaspase cDNA, NbMCA1, was amplified from Nicotiana benthamiana infected with Colletotrichum destructivum. It showed a peak in expression at 72 h post-inoculation corresponding with the switch to necrotrophy by C. destructivum. Inoculation of N. benthamiana with an incompatible bacterium, Pseudomonas syringae pv. tomato, which should induce a non-host hypersensitive response (HR), did not result in an increase in NbMCA1 expression at the time of necrosis development at 20-24 h postinoculation. Virus-induced silencing of NbMCA1 resulted in three to four times more lesions due to C. destructivum compared with leaves inoculated with the PVX vector without the cloned metacaspase gene or inoculated with water only. However, virus-induced silencing of NbMCA1 did not affect the HR necrosis or population levels of P. syringae pv. tomato. Although this metacaspase gene does not appear to be involved in the programmed cell death of non-host HR resistance to P. syringae, it does affect the susceptibility of N. benthamiana to C. destructivum indicating a function in a basal defense response. Possible roles of NbMCA1could be in degrading virulence factors of the pathogen, processing pro-proteins involved in stress responses, eliminating damaged proteins created during stress, and/or degrading proteins to remobilize amino acids to fuel de novo synthesis of proteins involved in stress adaptations.

Cloning of a cDNA encoding a cystatin from grain amaranth (Amaranthus hypochondriacus) showing a tissue-specific expression that is modified by germination and abiotic stress

A cDNA, encoding a cysteine protease inhibitor (AhCPI), was isolated from an immature seed cDNA library of grain amaranth (Amaranthus hypochondriacus L.) and characterized. It encoded a polypeptide of 247 amino acids (aa), including a putative N-terminal signal peptide. Other relevant regions found in its sequence included the G and PW conserved aa motifs, the consensus LARFAV sequence for phytocystatins and the reactive site QVVAG. The predicted aa sequence for AhCPI showed a significant homology to other plant cystatins. Gene expression analyses indicated that AhCPI was constitutively expressed in mature seeds, and gradually decreased during germination. In vegetative tissues, AhCPI was expressed in the radicle and hypocotyls of seedlings and in the stems and roots of young plantlets. Its expression in roots and stems increased substantially in response to water deficit, salinity-, cold- and heat-stress, whereas heat-stress induced a rapid and transient accumulation of AhCPI transcripts in leaves. The results obtained were suggestive of multiple roles for AhCPI in grain amaranth, acting as a regulator of seed germination and as a protective agent against diverse types of abiotic stress, which induced this gene in a tissue- and stress-specific manner. The work herewith described reports a novel, and apparently, single cystatin protein in which, in agreement with other plant model systems, could have a regulatory role in germination, and further expands previous findings linking the accumulation of protease inhibitors, mostly of the serine proteinase type, with protection against (a)biotic stress in A. hypochondriacus.

Sulfur metabolism in plants: are trees different?

Sulfur metabolite levels and sulfur metabolism have been studied in a significant number of herbaceous and woody plant species. However, only a limited number of datasets are comparable and can be used to identify similarities and differences between these two groups of plants. From these data, it appears that large differences in sulfur metabolite levels, as well as the genetic organization of sulfate assimilation and metabolism do not exist between herbaceous plants and trees. The general response of sulfur metabolism to internal and/or external stimuli, such as oxidative stress, seems to be conserved between the two groups of plants. Thus, it can be expected that, generally, the molecular mechanisms of regulation of sulfur metabolism will also be similar. However, significant differences have been found in fine tuning of the regulation of sulfur metabolism and in developmental regulation of sulfur metabolite levels. It seems that the homeostasis of sulfur metabolism in trees is more robust than in herbaceous plants and a greater change in conditions is necessary to initiate a response in trees. This view is consistent with the requirement for highly flexible defence strategies in woody plant species as a consequence of longevity. In addition, seasonal growth of perennial plants exerts changes in sulfur metabolite levels and regulation that currently are not understood. In this review, similarities and differences in sulfur metabolite levels, sulfur assimilation and its regulation are characterized and future areas of research are identified.

An insight into the sialotranscriptome of the seed-feeding bug, Oncopeltus fasciatus

The salivary transcriptome of the seed-feeding hemipteran, Oncopeltus fasciatus (milkweed bug), is described following assembly of 1025 expressed sequence tags (ESTs) into 305 clusters of related sequences. Inspection of these sequences reveals abundance of low complexity, putative secreted products rich in the amino acids (aa) glycine, serine or threonine, which might function as silk or mucins and assist food canal lubrication and sealing of the feeding site around the mouthparts. Several protease inhibitors were found, including abundant expression of cystatin transcripts that may inhibit cysteine proteases common in seeds that might injure the insect or induce plant apoptosis. Serine proteases and lipases are described that might assist digestion and liquefaction of seed proteins and oils. Finally, several novel putative proteins are described with no known function that might affect plant physiology or act as antimicrobials.

Construction and application of EST library from Setaria italica in response to dehydration stress

Foxtail millet is a gramineous crop with low water requirement. Despite its high water use efficiency, less attention has been paid to the molecular genetics of foxtail millet. This article reports the construction of subtracted cDNA libraries from foxtail millet seedlings under dehydration stress and the expression profile analysis of 1947 UniESTs from the subtracted cDNA libraries by a cDNA microarray. The results showed that 95 and 57 ESTs were upregulated by dehydration stress, respectively, in roots and shoots of seedlings and that 10 and 27 ESTs were downregulated, respectively, in roots and shoots. The expression profile analysis showed that genes induced in foxtail millet roots were different from those in shoots during dehydration stress and that the early response to dehydration stress in foxtail millet roots was the activation of the glycolysis metabolism. Moreover, protein degradation pathway may also play a pivotal role in drought-tolerant responses of foxtail millet. Finally, Northern blot analysis validated well the cDNA microarray data.

Identification of expression profiles of tapping panel dryness (TPD) associated genes from the latex of rubber tree (Hevea brasiliensis Muell. Arg.)

Tapping panel dryness (TPD) occurrence in high latex yielding rubber tree (Hevea brasiliensis) is characterized by the partial or complete cessation of latex flow upon tapping leading to severe loss in natural rubber production around the world. The goal of this study was to identify genes whose mRNA transcript levels are differentially regulated in rubber tree during the onset of TPD. To isolate TPD responsive genes, two cDNA libraries (forward and reverse) from total RNA isolated from latex of healthy and TPD trees were constructed using suppression subtractive hybridization (SSH) method. In total, 1,079 EST clones were obtained from two cDNA libraries and screened by reverse Northern blot analysis. Screening results revealed that about 352 clones were differentially regulated and they were selected for sequencing. Based on the nucleotide sequence data, the putative functions of cDNA clones were predicted by BLASTX/BLASTN analysis. Among these, 64 were genes whose function had been previously identified while the remaining clones were genes with either unknown protein function or insignificant similarity to other protein/DNA/EST sequences in existing databases. RT-PCR analysis was carried out to validate the up-regulated genes from both the libraries. Among them, two genes were strongly down-regulated in TPD trees. The level of mRNA transcripts of these two genes was further examined by conventional Northern and RT-PCR analysis. Results indicated that the expression level of two genes was significantly lower in TPD trees compared to healthy trees. Many TPD associated genes were also up-regulated in TPD trees suggesting that they may be involved in triggering programmed cell death (PCD) during the onset of TPD syndrome. The results presented here demonstrate that SSH technique provides a powerful complementary approach for the identification of TPD related genes from rubber tree.

Proregion of Acanthoscelides obtectus cysteine proteinase: a novel peptide with enhanced selectivity toward endogenous enzymes

Acanthoscelides obtectus is a devastating storage insect pest capable of causing severe bean crop losses. In order to maintain their own development, insect pest larvae feed continuously, synthesizing efficient digestive enzymes. Among them, cysteine proteinases (CPs) are commonly produced as inactive precursors (procysteines), requiring a cleavage of the peptide proregion to become active. The proregion fits tightly into the active site of procysteines, efficiently preventing their activity. In this report, a CP cDNA (cpao) was isolated from A. obtectus midgut larvae. In silico studies indicated that the complete CP sequence contains a hydrophobic signal peptide, a prodomain and a conserved catalytic region. Moreover, the encoding cDNA contains 963bp translating into a 321 residue protein, CPAo, which was expressed in E. coli, fused with thioredoxin. Enzymatic assays using the recombinant protein revealed that the enzyme was catalytically active, being able to cleave the synthetic substrate Z-Phe-Arg-7-AMC. Additionally, this report also focuses the cpao propeptide (PCPAo) subcloning and expression. The expressed propeptide efficiently inhibited CPAo, as well as digestive CP of other bean bruchids. Little or no activity was found against proteolytic enzymes of two other coleopterans: Rhyzopertha dominica and Anthonomus grandis. The data reported here indicate the possibility of endogenous propeptides as a novel strategy on bruchids control, which could be applicable to bean improvement programs.

Dinitro-o-cresol induces apoptosis-like cell death but not alternative oxidase expression in soybean cells

In plants, programmed cell death is thought to be activated during differentiation and in response to biotic and abiotic stresses. Although its mechanisms are far less clear, several morphological and biochemical features have been described in different experimental systems, including DNA laddering and cytosolic protease activation. Moreover, plant mitochondria have an alternative terminal oxidase (AOX), which is thought to be involved in protection against increased reactive oxygen species production, perhaps representing a mechanism to prevent programmed cell death. In this study, we analysed cell death induced by the herbicide dinitro-o-cresol (DNOC) in soybean (Glycine max) suspension cell cultures and evaluated biochemical and molecular events associated with programmed cell death. AOX capacity and expression were also determined. DNOC-treated cells showed fragmented nuclear DNA as assessed by an in situ assay that detects 3'-OH ends. In addition, specific colorimetric assays and immunoblot analysis revealed activation of caspase-3-like proteins and release of cytochrome c from mitochondria, respectively, confirming the apoptotic-like phenotype. Surprisingly, AOX capacity and protein levels decreased in DNOC-treated cells, suggesting no association between cell death and AOX under these experimental conditions. In conclusion, the results show that DNOC induces programmed cell death in soybean cells, suggesting that plants and animals might share similar pathways. Further, the role of AOX in cell death has not been confirmed, and may depend on the nature and intensity of stress conditions.

Characterization of a stress responsive proteinase inhibitor gene with positive effect in improving drought resistance in rice

A full-length cDNA gene, designated Oryza sativa chymotrypsin inhibitor-like 1 (OCPI1), was characterized in rice. The predicted protein of OCPI1 shows very high sequence identity to reported chymotrypsin inhibitors from various plant species. Northern-blot analysis showed that the expression of OCPI1 was strongly induced by dehydration stresses and abscisic acid (ABA). The expression of beta-glucuronidase (GUS) reporter gene under the control of OCPI1 promoter transformed into rice was strongly induced by drought and salt stresses. Interestingly, strong dehydration stress-induced GUS activity was also detected in the transgenic rice containing the reverse sequence of OCPI1 promoter fused to GUS gene, suggesting of a bidirectional transcriptional activity in the OCPI1 promoter. OCPI1 gene was over-expressed in japonica cv. Zhonghua 11 and transgenic plants containing single copy of transgene were tested for drought resistance at reproductive stage. The positive transgenic plants (OCPI1 was over-expressed) had significantly higher grain yield and seed setting rate than the wild type and the negative transgenic control (no over-expression of the transgene) under the severe drought stress conditions, whereas the potential yield of transgenic plants under normal growth conditions was not affected. Chymotrypsin-inhibitor activity assay showed that the crude protein of the positive transgenic plants had stronger inhibitory activity than the negative control. Transgenic plants had less decrease of total proteins than the wild type under drought stress. Taken together, these data indicate that OCPI1 might potentially be useful in the genetic improvement of drought resistance in rice.

Influence of jasmonic acid as potential activator of induced resistance against Karnal bunt in developing spikes of wheat

Induction of defense response against Karnal bunt (KB)by suppressing the pathogenesis was observed upon exogenous application of jasmonic acid (JA)as evident from decrease in the coefficient of infection and overall response value in both susceptible and resistant varieties of wheat. The ultra-structural changes during disease progression showed the signs of programmed cell death (PCD). However, JA strengthened the defense barrier by enhancing the lignifications of cell walls as observed in spikes of both varieties by histochemical analysis. Compared to the plants inoculated with pathogen alone, plants of resistant line (RJP) first treated with JA followed by inoculation with pathogen showed more lignifications and extracellular deposition of other metabolites on cells, which is supposed to prevent mycelial invasions. Contrary to this, susceptible (SJP)lines also showed lignifications but the invasion was more compared to resistant line. Induction of protease activity was higher in resistant variety than its corresponding susceptible variety. The protease activity induced during the colonization of the pathogen and its proliferation inside the host system gets inhibited by JA treatment as demonstrated by the quantitative and in-gel protease assay. The results indicate the role of JA signalling in inhibiting the proteases due to expression of certain protease inhibitor genes. SDS-PAGE analysis shows differential gene expression through induction and/or suppression of different proteins in wheat spikes of resistant and susceptible varieties under the influence of JA. Thus, exogenously applied JA provides the conditioning effect prior to the challenge of infection and induces defense against KB probably by maintaining a critical balance between proteases and protease inhibitors and/or coordinating induction of different families of new proteins.

Bioinsecticidal activity of Archidendron ellipticum trypsin inhibitor on growth and serine digestive enzymes during larval development of Spodoptera litura

The roles of serine proteases involved in the digestion mechanism of the cutworm Spodoptera litura (Lepidoptera: Noctuidae) were examined (in vitro and in vivo) following feeding of plant protease inhibitors. A trypsin inhibitor from Archidendron ellipticum (AeTI) was purified by ammonium sulfate fractionation, ion-exchange chromatography and size-exclusion chromatography (HPLC) and its bioinsecticidal properties against S. litura were compared with Soybean Kunitz trypsin inhibitor (SBTI). AeTI inhibited the trypsin-like activities of the midgut proteases of fifth instar larvae of S. litura by over 70%. Dixon plot analysis revealed competitive inhibition of larval midgut trypsin and chymotrypsin by AeTI, with an inhibition constant (K(i)) of 3.5x10(-9) M and 1.5x10(-9) M, respectively. However, inhibitor kinetics using double reciprocal plots for both trypsin and chymotrypsin inhibitions demonstrated a mixed inhibition pattern. Feeding experiments conducted on different (neonate to ultimate) instars suggested a dose-dependent decrease for both the larval body weight as well as % survival of larva fed on diet containing 50, 100 and 150 microM AeTI. Influence of AeTI on the larval gut physiology indicated a 7-fold decrease of trypsin-like protease activity and a 5-fold increase of chymotrypsin-like protease activity, after being fed with a diet supplemented with 150 microM AeTI. This study suggests that although the early (1st to 3rd) larval instars of S. litura are susceptible to the trypsin inhibitory action of AeTI, the later instars may facilitate the development of new serine proteases, insensitive to the inhibitor.

Towards identifying the full set of genes expressed during cassava post-harvest physiological deterioration

Storage roots of cassava (Manihot esculenta Crantz) exhibit a rapid post-harvest physiological deterioration (PPD) response that can occur within 24-72 h of harvest. PPD is an enzymatically mediated oxidative process with parallels to plant wound, senescence and defence responses. To characterise those genes that show significant change in expression during the PPD response we have used cDNA microarray technology to carry out a large-scale analysis of the cassava root transcriptome during the post-harvest period. We identified 72 non-redundant expressed sequence tags which showed altered regulation during the post-harvest period. Of these 63 were induced, whilst 9 were down-regulated. RNA blot analysis of selected genes was used to verify and extend the microarray data. Additional microarray hybridisation experiments allowed the identification of 21 root-specific and 24 root-wounding-specific sequences. Many of the up-regulated and PPD-specific expressed sequence tags were predicted to play a role in cellular processes including reactive oxygen species turnover, cell wall repair, programmed cell death, ion, water or metabolite transport, signal transduction or perception, stress response, metabolism and biosynthesis, and activation of protein synthesis.

Gliadain, a gibberellin-inducible cysteine proteinase occurring in germinating seeds of wheat, Triticum aestivum L., specifically digests gliadin and is regulated by intrinsic cystatins

We cloned a new cysteine proteinase of wheat seed origin, which hydrolyzed the storage protein gliadin almost specifically, and was named gliadain. Gliadain mRNA was expressed 1 day after the start of seed imbibition, and showed a gradual increase thereafter. Gliadain expression was suppressed when uniconazol, a gibberellin synthesis inhibitor, was added to germinating seeds. Histochemical detection with anti-gliadain serum indicated that gliadain was present in the aleurone layer and also that its expression intensity increased in sites nearer the embryo. The enzymological characteristics of gliadain were investigated using recombinant glutathione S-transferase (GST)-progliadain fusion protein produced in Escherichia coli. The GST-progliadain almost specifically digested gliadin into low molecular mass peptides. These results indicate that gliadain is produced via gibberellin-mediated gene activation in aleurone cells and secreted into the endosperm to digest its storage proteins. Enzymologically, the GST-progliadain hydrolyzed benzyloxycarbonyl-Phe-Arg-7-amino-4-methylcoumarin (Z-Phe-Arg-NH(2)-Mec) at K(m) = 9.5 microm, which is equivalent to the K(m) value for hydrolysis of this substrate by cathepsin L. Hydrolysis was inhibited by two wheat cystatins, WC1 and WC4, with IC(50) values of 1.7 x 10(-8) and 5.0 x 10(-8) m, respectively. These values are comparable with those found for GST-progliadain inhibition by E-64 and egg-white cystatin, and are consistent with the possibility that, in germinating wheat seeds, gliadain is under the control of intrinsic cystatins.

An approach to identify cold-induced low-abundant proteins in rice leaf

A proteomic approach has been adopted to investigate the low-abundant proteins in rice leaf in response to cold stress. Rice seedlings were exposed to different temperatures, such as 5 or 10 degrees C, and samples were collected after different time course. To eliminate the high-abundant proteins in leaf tissues such as ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), proteins were fractionated by polyethylene glycol (PEG). The elimination of Rubisco from the protein samples was confirmed by Western blot analysis. The PEG fractionated protein samples were separated by 2-DE and visualized by silver or CBB staining. A total 12 up-regulated protein spots were identified using the analysis of MALDI-TOF mass spectrometry or ESI MS/MS. We identified some novel proteins such as cysteine proteinase, thioredoxin peroxidase, a RING zinc finger protein-like, drought-inducible late embryogenesis abundant, and a fibrillin-like protein that had not yet been reported in the earlier reports on cold proteomic analysis. The identification of some novel low-abundant proteins in response to cold stress may provide a new homeostasis to develop enhanced cold tolerance transgenic plants. Thus, we propose that a PEG fractionation system can be used as an influential protein extraction method from the leaf samples, which can lead to knowledge of the expression pattern of low-abundant proteins in response to various biotic or abiotic stresses.

Cryptogein-induced anion effluxes: electrophysiological properties and analysis of the mechanisms through which they contribute to the elicitor-triggered cell death

Anion effluxes are amongst the earliest reactions of plant cells to elicitors of defence responses. However, their properties and their role in disease resistance remain almost unknown. We previously demonstrated that cryptogein, an elicitor of tobacco defence responses, induces a nitrate (NO(3) (-)) efflux. This efflux is an early prerequisite to the cryptogein-triggered hypersensitive response (HR). Here, we analyzed the electrophysiological properties of the elicitor-mediated NO(3) (-) efflux and clarified the mechanisms through which it contributes to cell death. Application of the discontinuous single electrode voltage-clamp technique in tobacco cells elicited with cryptogein enabled us to record the activation of slow-type deactivating anion channel currents. Cryptogein-induced plasma membrane depolarization and Ca(2+) influx, an essential component of elicitor signalling for HR cell death, were prevented by inhibiting the NO(3) (-) efflux. Similarly, pharmacological blocking of the anion efflux suppressed vacuolar collapse, a hallmark of cell death. The role of NO(3) (-) efflux in mediating proteases activation was further assessed. It is shown that cryptogein induced the activation of three proteases with apparent molecular masses of 95, 190 and 240 kDa. Their activation occurred independently on the anion efflux and, together with cell death, was strongly reduced by cycloheximide and the protease inhibitor PMSF. In contrast, the NO(3) (-) efflux was shown to promote the accumulation of transcripts encoding vacuolar processing enzymes, a family of proteases previously reported to contribute to the disruption of vacuole integrity observed during the HR. Collectively, our data indicate that anion efflux is an early prerequisite to morphological and biochemical events participating to cell death.

Uptake and translocation of metals in Spinacia oleracea L. grown on tannery sludge-amended and contaminated soils: effect on lipid peroxidation, morpho-anatomical changes and antioxidants

The plants of Spinacia oleracea L. grown on contaminated soil (CS) and different amendments of tannery sludge (TS) have shown high accumulation of metals in its edible part. The accumulation of toxic metal (Cr) in the leaves of the plants grown on CS was recorded as 40.67 microgg(-1)dw. However, the leaves of the plants grown on 100% TS have accumulated about two times (70.80 microgg(-1)dw) higher Cr than the 10% TS (31.21 microgg(-1)dw). Among growth parameters, the root length was more affected at 90 d than the shoot length, number of leaves and leaf area. The study of scanning electron micrographs showed 29.31% increase in stomatal length in the leaves of the plants grown on CS as compared to garden soil (GS), which served as control, however it decreased in the plants grown on higher amendments of TS. The decrease in MDA content at initial period of exposure and lower amendment was recorded in the leaves, whereas, significant increase (>10% TS onward) was observed with increase in tannery sludge ratio at 90 d as compared to GS. A coordinated increase in all the studied antioxidants (cysteine, non-protein thiol, ascorbic acid, carotenoid contents) was found up to 75 d of growth. At 90 d, most of the antioxidant decreased as compared to 75 d causing oxidative stress as evidenced by increased level of lipid peroxidation and decreased chlorophyll and protein contents. Maximum increase of 181.43% in MDA content and maximum decrease of 53.69% in total chlorophyll content was recorded in the leaves of the plants grown on 100% TS after 90 d of growth. The plants grown on CS have shown an increase in shoot length, number of leaves, leaf area, photosynthetic pigments and protein contents and in all the studied antioxidants. Thus, these plants are able to combat stress involving defense mechanism, resulting in healthy growth of the plants. The results are well coordinated as there is no change in the MDA content as compared to the plants grown on GS. In view of high Cr accumulation in edible part of S. oleracea grown on CS after irrigation with tap water, it is not advisable to use these plants for edible purposes. Summing up, it is recommended that the level of metals in the edible part should be checked instead of healthy growth as deciding parameter for consumption. It is demonstrated through this study that metal enriched plants have detoxification mechanism and grow well on organic matter enriched contaminated soil.

A Phytophthora infestans cystatin-like protein targets a novel tomato papain-like apoplastic protease

There is emerging evidence that the proteolytic machinery of plants plays important roles in defense against pathogens. The oomycete pathogen Phytophthora infestans, the agent of the devastating late blight disease of tomato (Lycopersicon esculentum) and potato (Solanum tuberosum), has evolved an arsenal of protease inhibitors to overcome the action of host proteases. Previously, we described a family of 14 Kazal-like extracellular serine protease inhibitors from P. infestans. Among these, EPI1 and EPI10 bind and inhibit the pathogenesis-related (PR) P69B subtilisin-like serine protease of tomato. Here, we describe EPIC1 to EPIC4, a new family of P. infestans secreted proteins with similarity to cystatin-like protease inhibitor domains. Among these, the epiC1 and epiC2 genes lacked orthologs in Phytophthora sojae and Phytophthora ramorum, were relatively fast-evolving within P. infestans, and were up-regulated during infection of tomato, suggesting a role during P. infestans-host interactions. Biochemical functional analyses revealed that EPIC2B interacts with and inhibits a novel papain-like extracellular cysteine protease, termed Phytophthora Inhibited Protease 1 (PIP1). Characterization of PIP1 revealed that it is a PR protein closely related to Rcr3, a tomato apoplastic cysteine protease that functions in fungal resistance. Altogether, this and earlier studies suggest that interplay between host proteases of diverse catalytic families and pathogen inhibitors is a general defense-counterdefense process in plant-pathogen interactions.

Reactive oxygen species, nitric oxide, and their interactions play different roles in Cupressus lusitanica cell death and phytoalexin biosynthesis

Beta-thujaplicin Is a natural troponoid with strong antifungal, antiviral, and anticancer activities. Beta-thujaplicin production in yeast elicitor-treated Cupressus lusitanica cell culture and its relationships with reactive oxygen species (ROS) and nitric oxide (NO) production and hypersensitive cell death were investigated. Superoxide anion radical (O2*-) induced cell death and inhibited beta-thujaplicin accumulation, whereas hydrogen peroxide (H2O2) induced beta-thujaplicin accumulation but did not significantly affect cell death. Both elicitor and O2*- induced programmed cell death, which can be blocked by protease inhibitors, protein kinase inhibitors, and Ca2+ chelators. Elicitor-induced NO generation was nitric oxide synthase (NOS)-dependent. Inhibition of NO generation by NOS inhibitors and NO scavenger partly blocked the elicitor-induced beta-thujaplicin accumulation and cell death, and NO donors strongly induced cell death. Interaction among NO, H2O2, and O2*- shows that NO production and H2O2 production are interdependent, but NO and O2*- accumulation were negatively related because of coconsumption of NO and O2*-. NO- and O2*- -induced cell death required each other, and both were required for elicitor-induced cell death. A direct interaction between NO and O2*- was implicated in the production of a potent oxidant peroxynitrite, which might mediate the elicitor-induced cell death.

Fusaric acid induces apoptosis in saffron root-tip cells: roles of caspase-like activity, cytochrome c, and H2O2

Programmed cell death (PCD), now known as apoptosis, is accompanied by specific morphological features. In this study, fusaric acid, a fusarium mycotoxin, was used to examine cell death in saffron (Crocus sativus Linnaeus) roots, using several apoptosis assays. Our results show that moderate FA doses (50-100 microM) induce apoptotic features while high FA doses (> 200 microM) stimulate necrosis. The apoptotic-like features induced by moderate doses of FA include chromatin condensation, formation of condensed chromatin spheres which bud from the nucleus, fragmentation of nucleosomal DNA into approximately 180 bp fragments, exposure of phosphatidyl serine to the external membrane leaflet, delivery of cytochrome c to cytosol, and generation of H(2)O(2). These apoptotic alterations in root cells are not observed in the presence of serine protease, caspase-1 or caspase-3 inhibitors. It is proposed that production of H(2)O(2) and release of cytochrome c into the cytosol may activate caspase-like proteases and thus establish the apoptotic pathway. As nuclei budding spheres formed in plant root cells after exposure to 50-100 microM FA doses seem to be digested inside the cytosol, we suggest labeling them as internal apoptotic bodies (IAB) that may be more informative than previously used term, apoptotic-like bodies.

The rice tapetum degeneration retardation gene is required for tapetum degradation and anther development

In flowering plants, tapetum degeneration is proposed to be triggered by a programmed cell death (PCD) process during late stages of pollen development; the PCD is thought to provide cellular contents supporting pollen wall formation and to allow the subsequent pollen release. However, the molecular basis regulating tapetum PCD in plants remains poorly understood. We report the isolation and characterization of a rice (Oryza sativa) male sterile mutant tapetum degeneration retardation (tdr), which exhibits degeneration retardation of the tapetum and middle layer as well as collapse of microspores. The TDR gene is preferentially expressed in the tapetum and encodes a putative basic helix-loop-helix protein, which is likely localized to the nucleus. More importantly, two genes, Os CP1 and Os c6, encoding a Cys protease and a protease inhibitor, respectively, were shown to be the likely direct targets of TDR through chromatin immunoprecipitation analyses and the electrophoretic mobility shift assay. These results indicate that TDR is a key component of the molecular network regulating rice tapetum development and degeneration.

The reactive oxygen species network pathways:an essential prerequisite for perception of pathogen attack and the acquired disease resistance in plants

Availability of complete Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) genome sequences, together with molecular recourses of functional genomics and proteomics have revolutionized our understanding of reactive oxygen species (ROS) signalling network mediating disease resistance in plants. So far, ROS have been associated with aging, cellular and molecular alteration in animal and plant cells. Recently,concluding evidences suggest that ROS network is essential to induce disease resistance and even to mediate resistance to multiple stresses in plants. ROS are obligatory by-products emerging as a result of normal metabolic reactions. They have the potential to be both beneficial and harmful to cellular metabolism. Their dual effects on metabolic reactions are dosage specific. In this review we focus our attention on cellular ROS level to trigger beneficial effects on plant cells responding to pathogen attack. By exploring the research related contributions coupled with data of targeted gene disruption, and RNA interference approaches, we show here that ROS are ubiquitous molecules of redox-pathways that play a crucial role in plant defence mechanism. The molecular prerequisites of ROS network to activate plant defence system in response to pathogen infections are here underlined. Bioinformatic tools are now available to scientists for high throughput analysis of cellular metabolisms. These tools are used to illustrate crucial ROS-related genes that are involved in the defence mechanism of plants. The review describes also the emerging findings of ROS network pathways to modulate multiple stress resistance in plants.

Characterization of cysteine proteases in Malian medicinal plants

Extracts form 10 different Malian medicinal plants with a traditional use against schistosomiasis were investigated for their possible content of proteolytic activity. The proteolytic activity was studied by measuring the hydrolysis of two synthetic peptide substrates Z-Ala-Ala-Asn-NHMec and Z-Phe-Arg-NHMec. Legumain- and papain-like activities were found in all tested crude extracts except those from Entada africana, with the papain-like activity being the strongest. Cissus quadrangularis, Securidaca longepedunculata and Stylosanthes erecta extracts showed high proteolytic activities towards both substrates. After gel filtration the proteolytic activity towards the substrate Z-Ala-Ala-Asn-NHMec in root extract of Securidaca longepedunculata appeared to have Mr of 30 and 97kDa, while the activity in extracts from Cissus quadrangularis was at 39kDa. Enzymatic activity cleaving the substrate Z-Phe-Arg-NHMec showed apparent Mr of 97 and 26kDa in extracts from roots and leaves of Securidaca longepedunculata, while in Cissus quadrangularis extracts the activity eluted at 39 and 20kDa, with the highest activity in the latter. All Z-Phe-Arg-NHMec activities were inhibited by E-64 but unaffected by PMSF. The legumain activity was unaffected by E-64 and PMSF. The SDS-PAGE analysis exhibited five distinct gelatinolytic bands for Cissus quadrangularis extracts (115, 59, 31, 22 and 20kDa), while two bands (59 and 30kDa) were detected in Securidaca longepedunculata extracts. The inhibition profile of the gelatinolytic bands and that of the hydrolysis of the synthetic substrates indicate the cysteine protease class of the proteolytic activities. Several cysteine protease activities with different molecular weights along with a strong variability of these activities between species as well as between plant parts from the same species were observed.